Extreme pressure lubricant



Patented Sept. 1, 1942 UNITED STATES PATENT OFFICE EXTREME PRESSURE LUBRICANT Willem Johannes Dominicus van Dijck; The

Hague, Netherlands, assignor, by mesne assignments, to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Application April 3, 1934, Serial No. 718,876. In the Netherlands April 4, 1933 6 Claims.

tures under which ordinary lubricants are no longer able to keep the moving surfaces apart. Such conditions develop, for example, in steel-mill rolling necks, universal joints and especially in the use of worm and hypoid gears in automobile transmissions. It is known that in such cases ordinary lubricating films fail to give satisfactory protection, and use is made of thin layers, of the order of molecular dimensions, of chemical compounds formed on and from the metal of the rubbing parts. It is thought that some of the substances, such, for example, as sulphur, chlorine, etc. when added to lubricating oils and subjected to high temperatures produced by the pressure on moving parts, combine in some chemical manner with the metal of these parts, producing microscopic protective films which adhere tenaciously to metal surfaces. to-metal contact when the oil film breaks under extremely high pressures and its function of lubricating metal surfacesis performed by the dense protective film formed on the metal'surfaces.

One of the essential requirements to be satisfied by these protective films is that their internal cohesion and contingently their external adhesion be less than that of the metal underneath said surfaces, so that on the whole or part of the protective film being swept away, the metal of the moving parts is not abraded.

In the technique of modern lubrication the protecting films referred to are generated from substances added for that purpose to extreme pressure lubricants. Such lubricants consist usually of blends of a petroleum cil'with a saponifiable oil, containing chemically combined sulphur or chlorine, or both, in the form of some of their compounds. "It has also been proposed to use lead soaps in the presence of sulphur for the same purpose. However, the hitherto known active ingredients of high pressure lubricants, from which the afore-mentioned compounds are formed continuously on metal surfaces of rubbing parts, have the drawback of a strong corroding action on the material of these moving parts, especially when moisture is present.

I have discovered that, instead of or in conjunction with sulphur and chlorine, or their derivatives, other elements, such, for example, as phosphorus, arsenic, selenium and tellurium and/or their organic or certain inorganic compounds can be used to impart highly desirable This prevents metalproperties to lubricating oils or greases used under severe pressure conditions. These elements .are closely related and maybe defined as metalloids of V and VIgroups of the periodic system having atomic weights in the ranges 31- 75 and 79-128, respectively.

According to my invention, one can use small quantities of either elemental phosphorus, arsenic, selenium or tellurium, or such inorganic compounds'as oxides and/or sulphides and/or selenides of phosphorus and/or those of arsenic, oxides and/or sulphides of selenium, and/or oxides of tellurium. These elements or their compounds can be admixed to lubricants, such as distilled or residual mineral oils or alkali, or lead, or aluminum soap-mineral oil greases, or animal or vegetable oils, so that they are uniformly and colloidally distributed throughout the mass of the lubricant; or the lubricant containing one or several of these substances may be subjected to heating, usually not above 100' 0., in order to cause these active ingredients of the lubricant to react chemically therewith, thus further activating the lubricant, i. e. producing within it the compounds which possess a property of forming protective lubricating films on sliding metal surfaces. For example, 100 parts by weight of castor oil and about 4 parts by weight of phosphorus pentoxide are heated in asteam bath. At about 70 C. a rapid reaction sets in producing a.yellow oily substance containing phosphoric acid partly esterified with castor oil. This product is immediately available for use as a lubricant under very high pressures and at high speeds, or it may be blended with a mineral oil, for which purpose it is first heated to about 170 C. in order to render it more readily soluble.

An excellent extreme pressure lubricant is obtained by mixing phosphorus trioxide with a mineral lubricating oil. P203 is miscible with mineral oil in every proportion, but it was found that a quantity of from one to two per cent. by

weight of P203 dissolved in lubricating oil is sufficient to ensure an entirely satisfactory product.

I have also found, that besides above mentioned elements and their inorganic compounds,

certain organic derivatives of these elements are particularly suited as active ingredients of extreme pressure lubricants. Among'such organic -derivatives, esters of phosphoric, phosphorous,

(R)2HPO4, etc. in which R represents either analkyl or aryl radical (halogenated or not) are within the scope of this invention. Similar esters can be derived from other acids mentioned hereinbefore. While substantially any esters (ordinary or mixed) of these acids are useful for improving to some extent lubricating properties of oils and greases, I prefer to employ esters of the described inorganic acids resulting from replacing in these acids one or more of their hydrogen atoms with the corresponding number of straight chain saturated alkyl radicals preferably containing at least eight carbon atoms. Illustrative examples of such esters are monoand/or dl, and/or tri-octyl phosphates, or monoand/or diand/or tri-cetyl phosphates, or similar neutral or acid esters of ceryl and/or miricyl or similar higher alcohols and hereinbefore disclosed acids, such as ceryl arsenates or arsenite, ceryl acid arsenates or arsenites, miricyl ortho-, meta-, or pyro-phosphates, miricyl acid phosphates or phosphites, etc. Similar and other esters of acids of phosphorus, arsenic, selenium and tellurium can be used. Effective quantities of such esters may-vary from less than 1% up to 15% or more. Lubricating properties of these esters permit their use as lubricants without the addition of lubricating oils or any other lubricating components or diluents. The following data illustrate the effect of some of such esters upon lubricating properties of a mineral oil:

Table Timken test in lbs/sq. in.

Lubricant Satisfactory Faded Mid-Continent steam refined stock.- 6, 715 8, 575 5% by volume of tri-iso-amyl phosphite added.. 25,000 28, 570 5% by volume of tri-butyl phosphite added 37, 140 40, 000 5% by volume of tri-cthyl phosphite added 28, 570 31, 420 3% by volume of n. butyl phosphate added 20, 000 28, 860 by volume of n. butyl phosphate added 22, 860 25, 700 10% by volume of tri-o-cresyl phosphate added 17, 140 20, 000 by volume of tri-o-cresyl phosphate added 22, 860 25, 700

attached to the carboxylic group are of about the same length, as for example in hexadecylor cetyl stearates, or palmitates, or oleates, which, I have found, are far superior to ethyl, butyl, or phenyl estersof the same fatty acids, The esters of my invention, when used in concentrations similar to those of the lower esters, are often twice as effective as the latter in lowering the coefficient of friction of metal surfaces under high pressures and also in raising the critical pressure limit of extreme pressure lubricants, as tested by known methods, such as Timken test. The essential characteristic of my active lubricant ingredients is that the radicals R1 and R2 in the formula RlCOORfl, representing fatty acid esters, have approximately equal numbers of carbon atoms; for obtaining the best results the difference should not be greater than, say, 50%, or still better not greater than of the shorter radical. For example, I prefer to use such esters of palmitic acid (for which R=15), as octyl palmitate, or nonyl, or decyl, or dodecyl, or ceryl, or miricyl palmitates; only nonyl or higher alkyl radicals should be combined with the stearate radical of stearic acid. By the higher fatty acids, from which my active esters can be derived, are meant aliphatic acids, either saturatedor unsaturated only to a relatively small degree (having not more than one double bond per molecule) and having at least eight carbon atoms per molecule. The esters may be chlorinated, if desired. The alkyl radical designated in theabove formula by R: preferably should be a straight chain grouping; side chains in this radical usually lessen to some degree, although not entirely eliminating the effectiveness of the ester as an active ingredient in extreme pressure lubricants.

It is, of. course. understood that this invention is in no way limitedto the examples given, and consists, briefly restated, in the discovery of the fact that high-grade extreme pressure lubricants may be obtained by the addition to lubricating mineral, animal or vegetable oils or lubricating greases (either of soda, lime, lead, or aluminum base) of substances like phosphorus, arsenic, selenium, or esters containing these elements, or their inorganic compounds, or certain esters of organic acids, preferably of the straight chain type and having eight or more carbon atoms. Extreme pressure lubricants obtained according to this invention and operating under service conditions do not froth obiectionably, are non-corrosive with copper, bronze and steel, and prevent excessive wear and scufllng of gears and bearings, since, as already stated, the internal cohesion and contingently the external adhesion of the molecular film formed between moving metallic surfaces is less than that of the metallic bod'yf underneath these moving surfaces.

Without departing from the spirit of this invention, other ingredients may also be added to increase the tenacity of the resulting lubricant and prevent leakage from bearings or'gear cases. For instance, a mineral lubricating oil containing phosphorus esters could also contain aluminium stearate, soda soaps, lead soaps or calcium soaps, and/or either raw or vulcanized rubber.

I claim as my invention:

1. A lubricant for metallic bearing surfaces comprising a,major proportion of lubricating oil and a minor proportion of the reaction product of castor oil and an oxide of phosphorus.

2. A lubricant for metallic bearing surfaces comprising a major proportion of lubricating oil and a minor proportion of the reaction product of castor oil and phosphoruspentoxide.

3. A lubricant for metallic bearing surfaces comprising a major proportion of lubricating oil and a minor proportion of a member of the group consisting of reaction products of fatty oils and oxides of phosphorus, organic esters ofthe acids of arsenic, selenium and tellurium, oxides, sulfides and selenides of phosphorus and aresenic, oxides and sulfides of selenium and oxides of tellurium.

4. A lubricant for metallic bearing surfaces WILLEM JOHANNES DOMINICUS VAN DIJCK. 

